Showing papers by "Ilinca Stanciulescu published in 2019"

The Running-in Micro-Mechanism and Efficient Work Conditions of Cu-Based Friction Material against 65Mn Steel

Abstract: In order to investigate the running-in process of a dry friction pair made of Cu-based powder metallurgy material and 65Mn steel, well designed pin-on-disc tests are carried out. According to the running-in mechanism of Cu-based powder metallurgy material in the tests, the running-in process is divided into two periods, namely, the interface matching period and the plastic deformation period. Then, two division indexes (the average height Sa and the root mean square height Sq) are introduced as basis for dividing this two periods, which originate from the extraction and analysis of surface morphology of asperities on the contacting surface. In the same way, two running-in recognition indexes, including equivalent changing rate H and coefficient of variation D, are further put forward as measures to characterize the running-in progress, and their effectiveness is verified by tests. Based on the recognition indexes H and D, the influence of temperature, rotation speed and load on the running-in duration of the dry friction pair is studied, and the efficient condition of running-in process is obtained. The results show that, when H ≤ 1.9 × 10−3 and D ≤ 4.2 × 10−2, we can recognise that the running-in process is completed. The running-in duration is almost the shortest under the condition of (40 N, 1400 r/min, 160 °C), which is called the efficient running-in condition.

Nonlinear Buckling and Postbuckling of Shallow Arches With Vertical Elastic Supports

Abstract: This paper presents an analytical method to investigate the effects of symmetric and asymmetric elastic supports on the nonlinear equilibria and buckling responses of shallow arches. It is found that arches with symmetric elastic supports can bifurcate into secondary paths with high-order symmetric modes. When a small asymmetry exists in the elastic supports, the equilibria of the arch may abruptly split and lead to the occurrence of remote unconnected equilibria. Such unconnected equilibria can be obtained experimentally or numerically using typical path following controls only with prior knowledge of location of these paths. A small asymmetry in the elastic supports may also make a secondary branch shrink into points connecting surrounding equilibria, resulting in the appearance of more limit points. The analytical solutions are also derived to directly calculate critical loads. We find that the magnitude of the stiffness of symmetric elastic supports has no influence on limits loads and bifurcation loads at branching into secondary paths with symmetric configurations, but greatly affect the bifurcation loads of secondary paths with asymmetric configurations. All critical loads are very sensitive to the degree of asymmetry in the elastic supports. The asymmetry in the supports reduces the top values of all pairs of critical loads compared to the case of symmetric elastic supports. The results obtained from the analytical derivations are confirmed using finite element analysis (FEA).

Monolithic and Staggered Strategies Using Solid-Shell Formulations for Nonlinear Coupled Thermoelasticity

Abstract: In this work, monolithic and staggered schemes using a locking-free solid-shell element are proposed to analyze the behavior of thin-walled structural components subjected to combined therm...

Efficient analysis of shear wall-frame structural systems

Abstract: This paper aims to propose an efficient method to conduct the preliminary analyses of medium or high-rise wall-frame structural systems with vertically varying properties. To this end, a finite element is formulated to take the shear deformation of the shear wall and the constrained moment of the link beam.,The differential equation of the structure is derived from the total potential energy. Its homogenous solutions are functions of initial parameters (deflections and inner forces). To solve the structure with vertically non-uniform properties, the authors first use the classical Timoshenko beam element and then heuristically propose a finite element that uses the initial parameter solutions as shape functions and is easier to implement. A post-processing method to compute the shear force in the frame and shear wall is developed. Modal analysis using the consistent mass matrix is also incorporated. Numerical examples demonstrate the accuracy and mesh independency of the proposed element.,The shear deformation of the shear wall and the constrained moment of the link beam significantly influence the static response of the structure. Taking into account the shear deformation can eliminate the misleading result of zero-base shear force of the frame and give much better predictions of the system natural frequencies.,The proposed method achieves higher accuracy than the classical approach most often used. The finite element formulation derived from transformations of the initial parameter solutions is simple and has superior numerical performance. The post-processing method allows for a fast determination of the shear force distributions in the shear wall and frame.

A note on the volumetric-deviatoric split on the anisotropic constitutive model for fiber-reinforced materials

Abstract: In the literature, it has been suggested that for a class of anisotropic constitutive laws for fiberreinforced materials, the volumetric-deviatoric split should only be performed on the isotropic (matrix) term, but not on the anisotropic (fiber) term. In this research note, we follow up on the theoretical and numerical analyses adopted in these early publications with an intuitive example that allows us to directly analyze the effect of this split. We demonstrate that performing such split on the anisotropic term leads to non-physical volume growth of the material sample. Therefore, we consolidate the observation that the volumetric-deviatoric split should not be applied to the anisotropic (fiber) term of the total strain energy.

On Euler Buckling and Snap-Through

Abstract: Bistable structures have seen significant attention in recent years for their potential uses in switching and energy harvesting. The behavior of these structures, however, is very sensitive to boundary conditions and initial geometry making their calibration for various applications a difficult task. Additionally, obtaining the force-deformation behavior of these highly (geometrically) nonlinear structures often requires computationally expensive continuation methods. This paper presents a very simple closed-form method which estimates several important characteristics of classical snap-through curves of transversely loaded beams. The estimation is based on a relationship between classic Euler buckling of beams under axial load and the snap-through of post-buckled and curved beams and arches under transverse loading that has recently been investigated by the authors.